Cigarette manufacturing has become a highly automated operation with tremendous effort going into the areas of efficiency and product quality. Cigarette making machines have been developed to operate at increasingly high-speeds, with machines now capable of running at production rates of up to 14,000 cigarettes per minute. However, as machine speeds have increased, it has become increasingly difficult to maintain product uniformity and high quality, because at such speeds even small variations in machine performance can alter the composition of the final product.
In order to maintain quality control, it is currently the practice to monitor certain properties of the final product. A number of product measurements are normally made, such as cigarette rod density, and compared to preestablished limits. If data values exceed the limits established, the diagnostic processor compiles a listing which is evaluated by personnel to attempt to determine the cause of the out-of-spec condition and what corrective action is needed.
In addition to monitoring the quality of the final product, it is also the practice to monitor the machine to ensure that it is operating normally. The state-of-the-art method for monitoring the operation of the machine involves the use of vibrational analysis.
In a typical vibration analysis diagnostic system, a frequency reference disk file is established which stores various frequencies of interest and amplitude limits. The frequencies of interest are based on the RPM harmonics of the major rotating and moving parts of the machine, as well as higher order vibrational frequencies. Amplitude limits are assigned to all frequencies and frequency ranges of interest based on data from the machine manufacturers, testing, and historical data.
When the machine is operating, vibration measurements are made at key locations on the machine using accelerometers and/or velocity transducers. The signals are then analyzed, using a Fast Fourier Transform ("FFT") analysis, to determine their harmonic frequencies. The theory of Fourier Frequency Analysis very basically is that a complex time domain wave form can be represented as a sum of individual sine waves. The application of this technique to the amplitude-versus-time wave produced by machines having multiple rotating parts results in a determination of the vibrational amplitude at various frequencies.
Each harmonic or range of harmonics in each sensor frequency spectrum is compared to the limit information in the frequency reference file. If one or more amplitudes exceed the limit for the respective frequency, a list of harmonic amplitude values and/or graph of the harmonic spectrum is generated, along with the parts which have corresponding harmonic frequencies. The spectral information is then interpreted by maintenance personnel or expert systems software to isolate the exact mechanical problem.
Vibrational analysis techniques provide frequency information concerning the condition of the various mechanical parts which generate the vibration, e.g., motors, bearings, component imbalance and misalignment, and component failures and impending failures can be identified using these techniques. However, such techniques do not provide quantitative information on the effect of the mechanical components on the tobacco stream. A mechanical component in the cigarette maker can exhibit a normal vibrational spectra and, through mis-adjustment, still adversely affect the tobacco stream. This condition is especially apparent in the cigarette maker hopper section due to the many rotating components involved in feeding the tobacco.
Similarly, measuring the properties of the product output does not provide sufficient information about the interrelated effects of mechanical parts on the manufacturing process, i.e., the tobacco stream, to optimize the rod making performance of cigarette makers.